Asthma Hospitalizations and Readmissions Among Children and Young
Adults -- Wisconsin, 1991-1995

Asthma is the most frequent reason for preventable hospital
admissions among children (1,2). During 1980-1993, national asthma
surveillance demonstrated increasing rates of hospital admission
for persons aged less than 25 years (3). These increasing rates
could be attributed to an increase in either the number of persons
admitted, readmitted, or both (4). To determine the number of
persons with asthma sufficiently severe to require hospitalization
and to characterize admission/readmission patterns for persons with
asthma, the Wisconsin Department of Health and Family Services
(WDHFS) analyzed data from the Wisconsin Asthma Surveillance System
(WASS). This report summarizes the findings from WASS, which
indicate that, during 1991-1995, an annual average of 18% of all
asthma admissions among Wisconsin residents aged less than 25 years
were readmissions.

WDHFS analyzed hospital discharge data from WASS to identify
all hospital admissions for asthma during 1991-1995 among Wisconsin
residents aged less than 25 years. In Wisconsin, all hospitals are
required to report discharge data to the state health department.
Admissions were considered asthma related if the primary diagnosis
was asthma (International Classification of Diseases, Ninth
Revision, Clinical Modification {ICD-9-CM}, code 493) or if the
primary diagnosis was respiratory illness (ICD-9-CM codes 460-496)
with a second or third diagnosis of asthma. In this analysis, the
number of asthma-related admissions does not equal the number of
persons admitted to a hospital for asthma because some persons were
readmitted for asthma during the specified time periods. An
admission was classified as a readmission if two or more database
entries matched on 1) hospital and medical record number or 2)
encrypted patient identifier, date of birth, sex, and zip code.
Transfer admissions were excluded from analysis. Race-specific
analyses were restricted to blacks and whites because numbers for
other racial groups were too small to calculate stable estimates.
Rates were age adjusted to the 1990 Wisconsin census. Denominators
for all rates were U.S. Bureau of the Census intercensal estimates
for Wisconsin.

During 1991-1995, a total of 11,804 Wisconsin residents aged
less than 25 years accounted for 17,678 hospital admissions for
asthma. Of these admissions, 82% had a primary discharge diagnosis
of asthma, 15% had a primary diagnosis of respiratory illness and
a second diagnosis of asthma, and 3% had a primary diagnosis of
respiratory illness and a third diagnosis of asthma. During this
5-year period, 33% of all asthma-related admissions were
readmissions, and 26% of the persons admitted for asthma accounted
for 51% of all asthma-related admissions.

During 1991-1995, the average annual number of asthma-related
admissions among persons aged less than 25 years was 3535; of
these, 616 (18%) were readmissions (Table_1). On average,
blacks
were five times more likely than whites to be admitted to a
hospital for asthma (64 versus 13 per 10,000 persons aged less than
25 years, pless than 0.001). For blacks and whites, readmissions
accounted for 23% and 15%, respectively, of all asthma-related
admissions. In addition, blacks were approximately 50% more likely
than whites to be readmitted to a hospital for asthma (19% versus
12%, pless than 0.001).

Based on age-specific data, the average annual number of
asthma-related admissions was highest for persons aged 0-4 years
(1661); of these, 384 (23%) were readmissions. In contrast, among
persons aged 5-14 years and 15-24 years, 13% and 12% of all
asthma-related admissions, respectively, were readmissions.

During 1991-1995, the annual asthma admission rate remained
relatively unchanged (Table_2). For each year of this period,
17%-18% of all asthma-related admissions were readmissions.

Editorial Note

Editorial Note: One national health objective for the year 2000 is
to reduce asthma admissions to less than 19 per 10,000 persons
(objective 11.1) (5). The data from WASS in this report indicate
that Wisconsin's asthma admission rate during 1991-1995 was 20
admissions per 10,000 persons aged less than 25 years. However,
using the number of persons admitted at least once for asthma in
the numerator rather than the number of admissions, the average
annual asthma admission rate during this period was 17 persons per
10,000. The percentage difference in these two rates (18%) resulted
from readmission of persons previously admitted for asthma during
the year.

Characterization of risk factors for asthma-related
readmission can enable development of interventions to prevent
readmissions. The high frequency of asthma-related admissions and
the disporportionate number of readmissions among blacks suggest
that efforts to reduce asthma-related admissions should target
persons who have been hospitalized for asthma. Previous studies
indicate that the race-specific differences in asthma admission
rates are associated with socioeconomic status (6,7).

The findings in this report are subject to at least two
limitations. First, erroneous data entry of any of the six
variables used to identify persons admitted to a hospital for
asthma could result in misclassification of an event as an incident
admission instead of a readmission. Similarly, patients who move
within the state may not be correctly identified as prevalent
cases.

The findings from WASS highlight the importance of analyzing
longitudinal, patient-specific data about asthma. Although most
states collect hospital discharge data that can be used for asthma
surveillance, few states have asthma surveillance programs (8).

Ongoing surveillance is necessary to assess the impact of
practice guidelines and interventions (9) to prevent asthma
hospitalizations. WASS can monitor the impact of intervention
efforts on asthma admission and readmission rates and the number of
persons requiring hospitalization for asthma. Patient-specific data
provide more detailed information about the burden of asthma than
admission data alone and can augment admission rates as a benchmark
in assessing progress toward improved management of asthma.

National Heart, Lung, and Blood Institute. National Asthma
Education and Prevention Program Task Force on the Cost
Effectiveness, Quality of Care, and Financing of Asthma Care.
Bethesda, Maryland: US Department of Health and Human Services,
Public Health Service, National Institutes of Health, 1996; DHHS
publication no. (NIH)55-807.

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